The invention relates generally to batteries, and more particularly to high performance batteries.
A typical battery includes one or more electrochemical cells which are electrically connected within the battery and provide the source of electrical power for the battery. These cells generally comprise four basic components: a positive electrode (anode on charge and cathode on discharge) that receives electrons from an external circuit as the cell is discharged; a negative electrode (cathode on charge and anode on discharge) that donates electrons to the external circuit as the cell is discharged; an electrolyte (often in a solution or paste) which provides a mechanism for electrical charge to flow between the positive and negative electrodes; and one or more separators which electrically isolate the positive and negative electrodes. This configuration enables the cell to generate electric power because of the electrochemical relationship of these components. Once the current is generated, it is typically carried from the positive electrode through a current carrier to a terminal, from where it is conveyed to the external circuit and back into the battery through a terminal connected with the negative electrode plate (typically through another current carrier).
With any battery, performance can be defined by certain parameters. These can include, inter alia, the voltage, current, and capacity of the battery. Obviously, the battery for a particular application should be designed with these parameters in mind.
One set of performance parameters that can present difficulty in achieving are those of a rechargeable high performance battery, such as that used for powering xe2x80x9chybridxe2x80x9d electric vehicles (i.e., vehicles that rely on both a battery-driven motor and an internal combustion engine for motive power), power tools and electric vehicles. Such batteries typically have low resistance so that current can be generated and provided to an external device very rapidly. Also, it is typically desirable that such a battery, particularly when used in conjunction with a hybrid vehicle, have a relatively low weight, and that it accept charge easily and rapidly.
In the cells of a high performance battery, the electrode plates, the electrolyte, and the separators should be selected such that the electrochemical relationship between these components can provide the desired current level in an acceptable discharge duration; of course, it would be desirable if such a battery were able to utilize currently available materials. Also, the cells should provide a current flow path from the electrode plates to and out of the cell terminal with relatively low resistance. Further, it would be desirable for the cells to have a configuration that facilitates manufacturing thereof.
The invention is directed to a low capacity, low resistance, high power cell. As a first aspect, the invention is directed to a winding assembly for a battery. The winding assembly includes a positive electrode plate, a negative electrode plate, a separator sheet, and a current collector. The positive and negative plates and the separator sheet are wound in overlying relationship such that the separator sheet is positioned between the positive and negative plates, an exposed top edge of the positive electrode plate is spaced longitudinally from an adjacent unexposed top edge of the negative plate, and an exposed bottom edge of the negative electrode plate is spaced longitudinally from an unexposed bottom edge of said positive electrode plate. The current collector is connected to one of the exposed edges of one of the positive and negative electrode plates, and, accordingly, is spaced apart from the adjacent unexposed bottom edge of the other (i.e., the non-attached) electrode plate. The current collector includes a terminal mounting portion and a radially extending collecting web. The collecting web of the current collector includes a perimeter, at least one open-ended perimeter aperture located at the perimeter and extending radially inwardly therefrom, and at least one closed-end internal aperture positioned between the terminal portion and the perimeter. In this configuration, the current collector can facilitate current flow from the electrode plate to which it is attached through a terminal and into an external circuit, thus providing a cell with the ability to deliver high current quickly. Also, this configuration can simplify attachment of the current collector to an adjacent electrode plate by providing access for an attachment tool (such as a welding device) at both internal and perimeter locations on the current collector.
The winding assembly is particularly suitable for use with positive and negative electrode plates and current collectors formed of lead-containing materials. In one embodiment, the current collector includes multiple perimeter apertures, multiple internal apertures, or both (either or both of which can be spaced circumferentially equidistant from each other). Preferably, current collectors of the described configuration are attached at both ends of the winding assembly. Also, it is preferred that the winding be placed in a container and terminals added to the current collectors to form a cell for a battery.
As a second aspect, the invention is directed to a winding assembly for a cell which includes positive and negative electrode plates and a separator circumferentially wound as described above, as well as current collectors attached to the top edge of the positive electrode plate and to the bottom edge of the negative electrode plate. At least one of the current collectors is formed of a third material and includes a terminal mounting portion and a radially extending collecting web. The collecting web includes a collecting portion, at least one recessed area within the collecting portion, and an aperture positioned within the recessed area. In this configuration, the application of heat of a preselected temperature and duration can cause the recessed area and electrode plate edge to melt into a joint (due to similarity in thermal mass), while the collecting portion remains substantially unchanged in shape. As a result, attachment of the current collector to the adjacent electrode plate is facilitated.
As with the first aspect of the invention, the above-described winding assembly is particularly suitable for use with positive and negative electrode plates and current collectors formed of lead-containing materials. In one embodiment, the current collector includes multiple perimeter apertures, multiple internal apertures or both (either or both of which can be spaced circumferentially equidistant from each other). Preferably, current collectors of the described configuration are attached at both ends of the winding assembly. Also, it is preferred that the winding be placed in a container and terminals added to the current collectors to form a cell for a battery.
As a third aspect, the invention is directed to a cover assembly for a battery cell. The cover assembly includes an internal cover including a vent and an external cover attached to the internal cover in overlying relationship. The external cover includes a downwardly-extending rib positioned directly above the vent. The cover assembly further includes a flexible diaphragm positioned in the vent that includes a projection extending upwardly to contact the rib of the external cover. In this configuration, the interaction between the rib and the projection maintains the diaphragm in place in the vent so that electrolyte does not leak from the cavity of the cell, yet allows venting of the battery cavity should the pressure therein become excessive.